The invention relates in general to the manufacture of spoolable material, and more specifically, to determining the location of defects previously identified in a material during manufacture and the removal of the defect in post-manufacturing processing.
The manufacturing of optical fiber is well known and is described in part in U.S. Pat. No. 5,298,047 to Hart Jr., et al., which discloses the major steps in the manufacturing of optical fibers and is incorporated herein by reference.
The manufacturing of optical fiber involves drawing or pulling a strand of fiber from a molten cylinder of pure glass. A solid cylinder of pure glass typically referred to as a preform assembly is heated using a furnace by conventional means. A portion of the glass becomes molten and a thin strand of glass is drawn from the preform assembly to begin the process of forming an optical fiber. The optical fiber is monitored in real time by various quality control instruments, such as a diameter monitor measuring the optical fiber diameter as it is drawn. As the fiber is drawn from the molten cylinder, the fiber cools down and eventually encounters a capstan wheel and a series of take-up wheels. The fiber is then rolled onto a take-up spool accumulating the manufactured fiber.
The length of fiber that is wound on the take-up spool is measured in the prior art using an odometer. The optical fiber passes over the roller of the odometer allowing the odometer to measure the length of fiber passing over the roller. The usage of an odometer to measure length is well known in the art of manufacturing optical fiber, as well as manufacturing cables, copper wires, et cetera.
During the manufacturing process, defects occasionally occur in the optical fiber. The nature of the defect is not critical to the principles of this invention, but may include imperfect cross-sectional geometries, unacceptable variations in the diameter, and the presence of tiny air bubbles, known as airlines. The causes of such defects are varied, and include impurities in the glass, uneven heat conduction, too small or too great of a draw rate, et cetera.
During manufacturing, the system may be drawing optical fiber at a high rate (e.g., 10-30 meters/second). The take-up spool typically has a diameter of 600 mm and rotates at a high speed to take up the fiber at the required rate. Consequently, a few seconds at this draw rate corresponds to a length of many meters of the optical fiber and many rotations of the take-up spool. It is not uncommon for a defect to exist for a number of seconds, so that the defective section may be hundreds of meters long. The odometer provides real-time information concerning the length of the fiber to a control processor that also receives inputs regarding the fiber quality. Using the odometer readings, the process controller records in a memory the location of defects observed in the optical fiber.
To remove defects in the fiber after the manufacturing process, the spool can be removed from the system and placed on a rewinder. The rewinder unwinds the fiber on the take-up spool by winding it onto another spool. The fiber is unwound from the take-up spool until the defect is located using an odometer position, and the optical fiber is physically cut. The defective optical fiber is further unwound from the take-up spool and discarded. Once all the defective fiber is removed, the acceptable fiber is rewound on another spool and the process repeated.
The prior method of determining the location of the section containing the defect (henceforth, simply referred to as xe2x80x98defectxe2x80x99) during rewinding is based on the process controller noting the odometer reading at the beginning and end of the defect during the fiber draw. The recordation of the odometer reading is automated, so that when the quality control monitoring system detects a defect, the odometer is read. Once the defect is no longer detected, the odometer is again noted. Thus, information is maintained indicating the length at which the defect begins and ends. Additional quality related information may be continuously recorded as well.
Removal of defects also relies on an odometer during the rewinding process to locate the defect. The odometer readings obtained during manufacture are key to measuring the required distances to locate the beginning and ends of the defective section. Further, accurately replicating the distances during rewinding is key to accurately locating the defect during the defect removal process. The odometer measures the distances, typically based in meters, of the location to the defect and the location to the end of the defect. Because absolute distances are measured, these values are independent of the particular spool being used to unwind/rewind the fiber. Thus, the odometer measures the distances of the defect on the fiber, independent of the spool.
Two competing concerns are involved in the removal of the defects. First, the process should remove the entire length of the defect. Specifically, even a short portion of defective optical fiber not removed from the fiber can degrade the optical transmission characteristics of the remaining optical fiber. To ensure that all the defective optical fiber is removed, additional fiber is removed both before and after the location of the defect. These additional sections are called xe2x80x98cut out bandsxe2x80x99 and are of a fixed length. Second, it is desirable to minimize waste, and this is accomplished by minimizing the removal of acceptable fiber.
To ensure both concerns are effectively addressed, the location of the defects must be accurately noted and locatable during rewinding. However, inaccuracies exist in the odometer that measures the fiber. The readings of the odometer may be inaccurate if the fiber slips when moving over the roller. This depends, in part, on the tension on the fiber from the take-up spool pulling the optical fiber, condition of the capstan, condition of the capstan belt, condition of encoder, or condition of any other mechanical device used in recording length. The fiber exhibits some elasticity when being pulled and the tension on the fiber when unwinding for removing the defect should be within specified limits. For example, excess tension can cause minute stretching of the fiber, or worse, breakage. Although these inaccuracies are insignificant when working with short lengths (e.g., hundreds of meters), they are significant when working with long lengths (e.g., hundreds of kilometers). For example, if the cumulative inaccuracy between two odometers during spooling and rewinding is 0.1%, then the inaccuracy results in a length of 500 meters over a 500 kilometer length.
Thus, there is a need for more accurately measuring the location of a defect on a spool of optical fiber so that the defective section can be removed with reduced waste. The determination of the location of a defect should also account for the inherent inaccuracies that become more significant when measuring greater lengths of the optical fiber. Similar issues are also typically present in the manufacture of other spoolable materials and are also in need of more accurate determination of the location of defects in the material.
It is one objective of the present invention to define a method for indicating the location of a defect in a material as it is wound on a spool comprising the steps of winding the material onto a spool, monitoring the material for defects, and indicating the location of the fiber on the spool corresponding to where a defect in the material is located on the spool. This is accomplished by recording rotational data associated with the spool upon which the material is wound, and/or detecting a change in pitch of the material wound upon the spool.
It is another objective of the present invention to define a method for removing a defect in a material wound on a spool comprising the steps of unwinding the material from the spool, detecting an indication of a defect in the material wound about the spool, and removing portions of the material wound about the spool.
It is another objective of the present invention to define a method for removing a defect in a material wound by incorporating a cut-out band that comprises a fixed part and a rotational part, where the rotational part is based on the relative location of the defect from the end of the material.
It is another objective of the present invention to define an apparatus for winding the material onto a spool comprising a monitoring device in communication with the material for monitoring defects in the material as it is wound onto the spool, and an indicator in communication with the monitoring device, wherein the indicator indicates the location on the spool where a defect is present in the material by using rotational counts, detecting a change in pitch, or a combination thereof.
It is another objective of the present invention to define an apparatus for removing defective material from a spool comprising an unwinding device for unwinding the material from a spool and an indicator for indicating the location of the defective material, wherein the indicator indicates the location on the spool where a defect is present in the material by using rotational counts, detecting a change in pitch, or a combination thereof.